Poly(arylene sulfides) (hereinafter abbreviated as “PASs”) represented by poly(phenylene sulfide) (hereinafter abbreviated as “PPS”) are engineering plastics excellent in heat resistance, chemical resistance, flame retardancy, mechanical properties, electrical properties, dimensional stability and the like. The PASs are commonly used in a wide variety of fields such as electrical and electronic equipments and automotive equipments because they can be molded or formed into various kinds of molded or formed products, films, sheets, fibers, etc. by general melt processing processes such as extrusion, injection molding and compression molding.
As a typical production process of a PAS, is known a process in which a sulfur source is reacted with a dihalo-aromatic compound in an organic amide solvent such as N-methyl-2-pyrrolidone (hereinafter may be abbreviated as “NMP”). However, the PAS obtained by the conventional production process has such defects that it is insufficient in toughness such as flexural strength and flexural elongation and flash is easy to occur upon injection molding. In order to overcome these defects, a method of reacting the PAS with a silane coupling agent has been proposed. However, the PAS obtained by the conventional production process has been generally insufficient in reactivity with the silane coupling agent, so that it is difficult to achieve satisfactory results.
On the other hand, there have been known processes, in which an alkali metal hydrosulfide or a mixture of an alkali metal hydrosulfide and an alkali metal sulfide is used as a sulfur source in place of the alkali metal sulfide, and the sulfur source is subjected to a polymerization reaction with a dihalo-aromatic compound in the presence of an alkali metal hydroxide (for example, Japanese Patent Application Laid-Open No. 2-302436, Japanese Patent Application Laid-Open No. 5-271414 and Japanese Patent Publication No. 6-51792). According to these processes, however, it is difficult to set conditions for stably performing the polymerization reaction. In addition, it is difficult to inhibit side reactions, since a great amount of the alkali metal hydroxide is used in these production processes. Further, it is difficult to obtain a PAS improved in the reactivity with the silane coupling agent.
As a process for producing a PAS improved in the reactivity with the silane coupling agent, there has heretofore been proposed a production process of a poly(arylene sulfide) by using, as a sulfur source, an alkali metal sulfide (a1) or using an alkali metal hydrosulfide (a2) and an alkali metal hydroxide (a3) in a proportion of at most 1 in terms of a molar ratio of (a3)/(a2), which comprises Step I of mixing this sulfur source and an alicyclic amide compound (for example, NMP) into a mixed solution; Step II of conducting polymerization while adding dropwise a polyhalo-aromatic compound to the mixed solution; and then Step III of adding an alkali metal hydroxide into the system on and after the time the amount of the polyhalo-aromatic compound consumed amounts to at least 50%, thereby conducting a reaction (Japanese Patent Application Laid-Open No. 2001-181394).
According to the process disclosed in Japanese Patent Application Laid-Open No. 2001-181394, a PAS, which has many reaction-active sites and good affinity for the silane coupling agent, can be obtained. However, side reactions are easy to occur, and it is difficult to stably perform the polymerization reaction. In particular, it is difficult to obtain a PAS having a sufficiently high melt viscosity, since a process of only raising a polymerization temperature to continue the polymerization reaction is adopted though the alkali metal hydroxide is added in Step III. The melt viscosity of the PAS is used as an index to its molecular weight or polymerization degree, and a high melt viscosity is desired in order to provide a PAS excellent in toughness. Furthermore, a long-time polymerization reaction is necessary for providing a PAS having a desired melt viscosity according to the process disclosed in Japanese Patent Application Laid-Open No. 2001-181394.
There has been proposed a production process of a poly(arylene sulfide) by subjecting a sulfur source including an alkali metal hydrosulfide and a dihalo-aromatic compound to a polymerization reaction in an organic amide solvent and adding an alkali metal hydroxide into the mixture for polymerization reaction continuously or in portions to control the pH of the mixture for polymerization reaction within a range of from 7 to 12.5 from the beginning to the end of the polymerization reaction (Japanese Patent Application Laid-Open No. 2004-244619). According to this process, a PAS having a high purity and a high melt viscosity can be stably provided while inhibiting side reactions and decomposition reactions. However, the PAS obtained by this process is insufficient in the reactivity with the silane coupling agent.
There has been proposed a process for producing a poly(arylene sulfide) by polymerizing a sulfur source and a dihalo-aromatic compound in an organic amide solvent, which comprises (1) a dehydration step of heating and reacting a mixture containing the organic amide solvent, an alkali metal hydrosulfide and an alkali metal hydroxide in a proportion of 0.95 to 1.05 mol per mol of the alkali metal hydrosulfide to discharge at least a part of a distillate containing water from the interior of the system containing the mixture to the exterior of the system; (2) a charging step of adding an alkali metal hydroxide and water to the mixture remaining in the system after the dehydration step, as needed, in such a manner that the alkali metal hydroxide and water are present in proportions of 1.00 to 1.09 mol and 0.5 to 2.0 mol, respectively, per mol of a sulfur source (hereinafter referred to as “charged sulfur source”) including the alkali metal hydrosulfide; (3) a first-stage polymerization step of adding the dihalo-aromatic compound to the mixture to subject the sulfur source and the dihalo-aromatic compound to a polymerization reaction at a temperature of 170 to 270° C., thereby forming a prepolymer that a conversion of the dihalo-aromatic compound is 50 to 98%, and (4) a second-stage polymerization step of controlling the amount of water in the reaction system after the first-stage polymerization step so as to bring about a state that water is present in a proportion of 2.0 to 10 mol per mol of the charged sulfur source, and heating the reaction system to 245 to 290° C., thereby continuing the polymerization reaction (International Publication No. 2004/060972 Pamphlet).
According to the process disclosed in International Publication No. 2004/060972 Pamphlet, a PAS having a high melt viscosity and good reactivity with the silane coupling agent can be provided. Examples 1 to 3 of this document show that PASs having a melt viscosity of 110 to 145 Pa·s as measured at a temperature of 310° C. and a shear rate of 1216 sec−1 were obtained.
In International Publication No. 2004/060972 Pamphlet, “reactivity with AS” is adopted as an index to the reactivity with the silane coupling agent. Here, AS means γ-aminopropyltriethoxysilane (abbreviated as “aminosilane”). The reactivity with AS is represented by a ratio (MV2/MV1) of a melt viscosity (MV2) of the PAS as measured at a temperature of 310° C. and a shear rate of 1216 sec−1 after the PAS is reacted with γ-aminopropyltriethoxysilane (AS) to a melt viscosity (MV1) before the reaction. A higher ratio indicates that the PAS has better reactivity with the silane coupling agent. In this document, it is shown that the ratio (MV2/MV1) of the PASs obtained in Examples 1 to 3 is 2.2 to 2.5.
However, as to the process disclosed in International Publication No. 2004/060972 Pamphlet, there has been a room for improvement in sufficiently stable and efficient production of a PAS having a high melt viscosity and high reactivity with the silane coupling agent, since a process of charging the whole of a necessary amount of the alkali metal hydroxide in the charging step is adopted.